Electrostatic spray arrangement



March 29, 1960 O. GENGENBACH ETAL ELECTROSTATIC SPRAY ARRANGEMENT 2 Sheets-Sheet 1 Filed Nov. 23, 1956 INVENTORS OTTO GENGENBACH HORST SCHENE ATTORNEYS March 29, 1960 I o. GENGENBACH ETAL 2,930,350

ELECTROSTATIC SPRAY ARRANGEMENT 2 Sheets-Sheet 2 Filed Nov. 23, 1956 INVENTORS ATTORNEYS OTTO GENGENBACH HORST SCHENE United States Patent ELECTROSTATIC SPRAY ARRANGEMENT Otto Gengenbach and Horst Schene, Sindelfingen, Kreis Boeblingen, Germany, assignors to Daimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany Application November 23, 1956, Serial No. 623,967

Claims priority, application Germany November 26, 1955 15 Claims. (Cl. 118 627) The present invention relates to an installation for electrostatically covering large objects, especially vehicle bodies of motorvehicles, with paints, lacquer, enamel or the like.

The known electrostatically operating installations for coating spatially large objects which installations, for the most part, only represent a simple enlargement of the installation customary for smaller objects, occupy a disproportionately large space because of the large distances necessary for purposes of proper insulation of the electric spray installation from the stationary structural parts which carry the same- Consequently, the manufacture thereof involves considerable difficulties and costs which are further increased if either the object to be coated or the spray installation or both together, for purposes of achieving a uniform coating, must be constructed so as to be movable. Furthermore, in such installations oftentimes a considerable loss of the coating material takes place due to undesirable scattering or dispersion thereof.

All of these disadvantages of the prior art are avoided by the present invention.

The present invention consists in that a screen or shield made of insulating material and provided on both sides thereof with a metal coating or layer is arranged between the electric spray installation and the frame carrying the latter. The one metal layer of these two layers, which faces the spray installation is charged with elec tricity of the same polarity as the spraying device, however, preferably to a somewhat smaller voltage than the spraying device, whereas the other metal layer facing the frame is grounded. The insulating screen may be secured either at an insulating arm projecting outwardly from the frame and carrying at the free end thereof the spraying device or at separate supports which connect the screen with the grounded frame. In the latter case, the insulating arm carrying the spraying device is appropriately extended through a slot provided in the insulating screen which slot itself extends in the direction of the intended displacement of the spraying device in order to enable displacement along the frame of the insulating arm and therewith of the spraying device carried thereby. I In that case, the insulating arm is also provided with an additional screen made of insulating material and'covering the slot in order to prevent a scattering or. dispersion of the electric field lines and therewith an escape of the coating material during the spraying process through the slot.

The distance of the spraying device from the grounded frame carrying the same may be reduced by the teachings in accordance with the present invention to one half or less than one half the amount of this distance necessary without the insulating screen in accordance with the present invention. Consequently, the over-all dimensions and therewith the spatial requirements and costs connected therewith are very favorably affected by the application of the present invention to the known prior art installations.

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Simultaneously therewith a concentration of the electric field lines which extend from the spraying device to the object to be coated takes place as a-result of the connection of the high potential to the front metallic layer of the screen and therewith a sharply-defined localization of the spraying stream thereby lessening the danger of scattering and wasting spray material and of non-uniform coatings.

Accordingly, it is an object of the present invention to provide an electrostatic spray arrangement which may be made of relatively smaller dimensions and which reduces the cost of manufacture 'andinstallation as well as spatial requirements for its installation.

Another object of the present invention is to provide an electrostatic screen or shield which concentrates the electric field of the spray installation and therewith re- -duces losses due to scattering or stray spraying.

A still further object of the present invention is to provide an electrostatic spraying device which operates more efiiciently.

A still further object of the present invention is to -provide an electrostatic spray installation for motor' vehicle bodies which requires less space for the installation thereof.

These and other objects, features and advantages of the present invention will become more'obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one preferred embodiment in ac-" cordance with the present invention and wherein:

Figure 1 is a front view of an installation for electro-' statically coating a vehicle body in accordance with the present invention;

Figure 2 is a top plan view of the electrostatic spray installation illustrated in Figure 1;

Figure 3 is a front view of the upper or overhead spray installation in accordance with the present invention, par-, tially in cross section and on an enlarged scale, and

taken along line 3-3 of Figure 1; and

Figure 4 is a view partially in longitudinal cross sec-1 tion and on an enlarged scale of the spraying device properly speaking, together with the insulating arm carrying the, same on an'enlarged scale.

Referring now to the drawing wherein like reference numerals are used to designate like parts in the various views thereof, and more particularly to Figures 1 and 2' which illustrate a gantry-type frame for the electrostatic spray installation in accordance with the present invention, reference numerals 8 and 9 designate the upright supports or standards which are interconnected on top thereof by the cross bearer 10. The insulating arms 7 which carry as spray electrodes the spraying disks or' dishes 15 are movably guided on the supports or bearers 8, 9 and 10 in the direction of the arrows 30. The spraying disks or dishes 15 are electrically insulated by the insulating arms '7'from the metallic masses or members of the frame and therewith are insulated In addition thereto, an electric motor 22 provided with] reduction gear 22 is arranged at every insulating arm I which places into rotation the respective shaft 26 and the spray dish 15 secured to shaft 26 about the longitudinal axis thereof. Paint is continuously supplicd in liquid state to the spray dishes 15 through discharge orifice or nozzle 31 from a supply arrangement of any suitable? construction (not illustrated herein in greater de'tail)-. Under the influence of the centrifugal forces the paint 3 Y 3 injected against the dish 15 will distribute itself in an even thin layer over the concave inner surface of the respective spraying dish 15 and is thereby simultaneously charged to the electric potential of the spraying disk 15.

The object 13 to be coated with a paint cover, in the instant case, a metallic vehicle body for motor vehicles, is moved or conveyed in the longitudinal direction thereof and at a. predetermined speed on a conveying device 32 of suitable construction by means of which it is continuously connected electrically with ground, i.e., is moved in a direction transversely to the plane of the drawing, past the spraying dishes 15 while the spraying dishes 15 in turn are moved to and fro uniformly in the direction of the arrows 30 along the frames 8, 9 and 10.

Under the influence of the electrostatic high voltage field which exists between the spraying dishes 15, on the one hand, and the grounded vehicle body 13, on the other, the paint which follows the direction of the electric lines of force 33 issprayed off in a finely distributed spray from the edge of the spraying dishes 15 toward the surface of the vehicle body 13 whereby the latter is provided with an even paint coating. As described so far, hereinabove, the illustrated installation corresponds to well-known installations so that the particular details of the construction thereof need not be further described herein.

According to the present invention, screens or shields 11 made of insulating material are arranged between every spraying dish or disk 15 and the respective frame parts 8, 9 and 10 carrying the same, the screens 11 being connected with the grounded frame parts 8, 9 and 10 by means of struts 16 or the like. The screens 11 are provided with longitudinal slots 12 through which the insulating arms 7 with the spraying dishes project into the inner space of the installation formed by the frame.

Each of the insulating screens 11 is also provided on the front side thereof and on the rear side thereof with a thin metal cover or layer 11' and 11", respectively. The front metal covers or layers 11' are each connected over a line to the center tap of a voltage divider formed by series-connected resistances 26 and 26 which are connected between the high voltage source 23 and ground so that the front layer 11 is charged to a slightly lesser potential than the spraying dish 15; however, since the layer 11 is charged from the same source 23 of electricity as the spraying dish 15 it is charged with the same polarity relative to ground. For example, the high voltage source 23 and therewith the spraying dishes 15 may be charged to a potential of 100 kilovolts whereas the metal covers 11 are charged to a potential of 70 kilovolts with respect to ground. The rear metal cover 11" of each insulating screen 11 is connected to ground over a line 19.

For purposes of covering the slots 12 in the insulating screens 11, smaller covering screens 14, possibly also made of insulating material, are arranged at the insulating arms 7 in front of the screens 11. The smaller covering screens 14 prevent a scattering or straying of the electric field lines. through the slots 12 to the rear layer 11" of the insulating screen 11 or to the frame parts 8, 9 and 10. These covering screens 14 are also provided on the front side thereof with metal covers or layers 14 which are connected to the line 27 and therewith are charged to the same potential as the front covers 11 of the larger insulating screens 11.

Depending on the conditions of the size of the overall installation the insulating screens 11 may also be secured directly to the insulating arms 7 so that they are movable in unison together therewith. In that case the slots 12 in the insulating screens 11 and the additional covering screens: 14 may be dispensed with.

By arranging the insulating screens 11 between the spraying dishes Bend the frame parts 8, 9 and. 10, the distance of the spraying dishes from the frame parts and therewith the over-all dimensions of the entire. sprayinstallation may be considerably reduced without having to fear any disadvantageous influences of the grounded frame parts on the electric high-voltage field existing between the spraying disks or dishes 15 and the objects 13 to be coated and therewith on the intensity and uniformity of the spraying process. Quite to the contrary, experience has amply demonstrated that by the presence of an insulating screen in accordance with the present invention and charged to a high potential, a high concentration of the electrostatic field lines 33 and therewith a well-defined spraying stream is obtained so that the previously existing considerable losses in coating material, such as paint, by reason of scattering or stray-spraying of paint particles is effectively avoided.

While we have shown and described one preferred embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit of the present invention, and we intend to cover all such changes and modifications as defined by the appended claims.

We claim:

1. An installation for electrostatically coating large objects with coating material including a gantry-type metallic frame, said frame having generally vertically extending side supports and a horizontally extending top support, electric spray means including a spray electrode mounted on each of said supports, each of said spray means including means for supporting it on said frame including an insulating arm carrying said spray means, an insulating screen disposed rearwardly of each spray electrode between the frame and the spray means, said insulating screen being provided at least on one side thereof facing said spray electrode with a metallic layer that is thin relative its width and breadth and of large area relative the size of said spray electrode, electric means including a high voltage source for providing a high voltage electrostatic field between each said spray means and an object located centrally of the frame to be electrostatically coated, and means for connecting said metallic layer facing said spray electrode to said high voltage source with the same polarity as said spray electrode.

2. An installation according to claim 1, including on said screen a metallic layer facing said frame at the same potential as said frame.

3. An installation according to claim 2, wherein said frame is grounded.

4. An installation according to claim 1, wherein said means for supporting said spray means on said frame includes said insulating arm carrying at the free end thereof said spray means and wherein said screen is carried by said insulating arm, said insulating arm extending away from said frame.

5. An installation according to claim 1, wherein said means for supporting said spray means includes an insulating arm movable relative said frame and carrying said spray means and wherein said screen is secured to said frame and is provided with a slot through which said insulating arm extends to enable said insulating arm to carry out to-and-fro movements relative said screen in the direction of said slot, and separate means for supporting said screen at said frame.

6. An installation according to claim 5, further comprising a covering screen made of insulating material and covering said slot, said covering screen also being provided with a metallic layer facing said spray electrode, the metallic layer facing said spray electrode being charged with a voltage of the same polarity of the metallic layer on said first-mentioned screen facing said spray means.

7. An installation according to claim 1, wherein said electric means includes a source of high: voltage with one terminal thereofv connected to said spray means and the other terminal thereof grounded, said frame being also grounded, a voltage divider connected across said source,

coating large objects, comprising electric spray means in-' cluding a spray electrode, insulating means for supporting said spray means on said frame including between the frame and spray means an insulating screen provided on both sides thereof with ametallic layer, said insulating screen being disposed rearwardly of said spray electrode, means for charging said spray means from a source of high voltage with a high voltage of predetermined polarity with respect to said frame and the object to be electrostatically coated, and means for charging the metallic layer facing said spray means with electricity of said predetermined polarity, said metallic layers on said screen being thin relative their width and breadth.

9. An installation according to claim 8, wherein said frame and said object as well as the metallic layer facing said frame are grounded.

10. An installation according to claim 8, wherein said insulating means includes an insulating arm carrying at the free end thereof said spray means, and wherein said screens is directly supported on said insulating arm, said insulating arm extending in a direction away from said frame.

11. An installation according to claim 8, wherein said screen is secured to said frame and is provided with a longitudinal slot and wherein said insulating means includes an insulating arm movable relative bothsaid frame and said screen extending through said slotand carrying at the free end thereof said spray means,

and strut means for supporting said screen at said frame.

12. An installation according to claim 11, further comprising a covering screen supported in front of said firstmentioned screen to cover said slot.

13. An installation according to claim 12, wherein said covering screen further comprises a metallic layer facing said spray means, and means for energizing said lastmentioned layer with a voltage of the same polarity as the metallic layer of said first-mentioned screen also facing said spray means.

14. An installation according to claim 13, wherein said covering screen is carried directly by said insulating arm.

.15. An installation according to claim 14, further comprising a voltage divider connected between the highvoltage terminal of said source and ground, and wherein the metallic layers of said screen and covering screen facing said spray means are charged by the same polarity and with the same voltage from said voltage divider.

References Cited in the file of this patent UNITED STATES PATENTS 2,546,701 Ransburg et al. Mar. 27, 1951 2,632,716 Starkey Mar. 24, 1953 2,658,009 Ransburg Nov. 3, 1953 2,711,155 Starkey June 21, 1955 2,773,472 Lamm Dec. 11, 1956 FOREIGN PATENTS 749,008 Great Britain May 16, 1956 

